TLA 
PL A 
P L A 
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for these at the due distances, their places 
must be supplied with common stakes of dead 
wood. The hedge is to be first thinned, by 
cutting away all those shoots which are in- 
tended to be used either as stakes or the 
other work of the plashing : the ditch is to be 
cleaned out with the spade ; and it must be 
now dug as at first, with sloping sides each 
way; and when there is any cavity on the 
bank on which the hedge grows, or the earth 
has been washed away from the roots of the 
shrubs, it is to be made good by facing it, as 
they express it, with the mould dug from the 
upper part of the ditch : all the rest of the 
dearth dug out of the ditch is to be laid upon 
the top of the bank, and the owner should 
look carefully into it that this is done ; for the 
workmen, to spare themselves trouble, are 
apt to throw as much as they can upon the 
face of the bank; which being by this means 
overloaded, is soon washed oil' into the ditch 
again, and a very great part of the work un- 
done ; whereas, what is laid on the top of the 
bank always remains there, and makes a good 
fence of an indifferent hedge. 
PLASTER. See Pharmacy. 
Plasters are combinations of oils and me- 
tallic oxides destined to be spread upon 
leather or cloth, and in that state to be ap- 
plied as a covering of ulcers, &c. They 
pught to be solid bodies, not so hard as to re- 
fuse to spread easily and equally, nor so soft 
"gs to rup into oil when heated by the skin. 
They ought to admit of being easily kneaded 
When heated with the hand, to adhere firmly 
to tile skin, but to be capable of being re- 
jnioved without leaving behind them any 
stain. Without these properties they do not 
ans\yer the purpose for which they are des- 
tined, which is chiefly adhesion. 
The only chemist who has hitherto ex- 
amined plasters with attention is Deyeux, to 
whom we are indebted for some excellent 
observations on the method of preparing 
them. 
The oxides hitherto employed for making 
plasters are those of lead ; and litharge is 
usually considered as the best adapted for 
that purpose, of any of these oxides. But 
the oxides of several of the other metals, as 
bismuth and mercury, are also capable of 
forming plasters, and might perhaps in some 
cases be employed with advantage. Some 
metallic oxides, however, as those of iron, 
are not susceptible of that kind of combina- 
tion with oils which constitutes plasters. 
All the fixed oils are capable of forming 
plasters; but they do not all form plasters 
with the same properties. The drying.oils, 
linseed-oil for instance, form plasters of a 
much softer consistency than the fat oils ; 
but these last acquire the same properties as 
the drying oils, it they are combined with mu- 
cilage. Thus olive-oil, boiled for some time 
with linseed or fenugrec, forms with litharge 
plasters as soft as those composed of linseed- 
oil and litharge. According to Deyeux, 
olive-oil answers better for plasters than any 
other. 
'There are three different ways of forming 
plasters. The first consists in simply mixing- 
together od and litharge in proper propor- 
tions, and allowing the mixture to remain a 
considerable time in the common tempera- 
ture of the atmosphere, agitating it occasion- 
ally. The oxide gradually Ifses its colour, 
and combines with the oil, and the mixture 
acquires consistence. This process is tedious, 
and does not furnish plasters sufficiently solid 
to answer the purposes for which they are in- 
tended. It is not therefore employed. 
The second method consists in throwing 
the oxide into the oil while boiling. Piasters 
formed by this process have always a deep 
colour, and a peculiar odour, occasioned by 
the decomposition of a portion of the oii. 
When this process is followed, it is necessary 
that the oxide should be in the state of a fine 
powder ; and that by agitation it should be 
made to combine with the oil as fast as pos- 
sible, otherwise the metal will be revived 
altogether, in consequence of the strong tend- 
ency which oil has to combine with oxygen 
when raised to a high temperature. 
The third method is most frequently prac- 
tised, because it is not liable to the same in- 
conveniences as the other two. This method 
consists in boiling the oil and the oxide toge- 
ther in a sufficient quantity of water. Ry this 
liquid the heat is moderated at first till the 
oil and oxide combine, which prevents the 
revival of the metal; and afterwards when 
the water is dissipated, the temperature is 
sufficiently high to give the plaster the requi- 
site consistency. 
Plasters, when long kept, become often too 
hard to be fit for use, especially if the requi- 
site proportion of oil has not been employed 
at first. This defect is easily remedied, by 
melting them with a small portion of new oil. 
Plasters, when long kept, likewise change 
their colour, and most of their sensible pro- 
perties; owing either to the absorption of 
oxygen, or to some change produced in their 
component parts by the action of the air. 
PLASTIC E, the plastic art, a branch of 
sculpture, being the art of forming figures of 
men, birds, beasts, fishes, &c. in plaister, 
clay, stucco, or the like. See Sculpture. 
Plastice differs from carving in this, that 
the figures are made by the addition of what is 
wanting ; but in carving always by subtract- 
ing what is superfluous. The plastic art is 
now chiefly used among us in fret-work ceil- 
ings ; but the Italians apply it also to the 
mantlings of chimneys with great ligures. 
PLATA LEA, the spoonbill, in ornitho- 
logy, a genus belonging to the order of grai- 
ls. The beak is plain, and dilates towards 
the point into an orbicular form; the feet 
have three toes, and are half-palmated. There 
are three species, distinguished by their co- 
lour : and of these species there are three va- 
rieties ; two of which are called the white spe- 
cies, and one of the roseate. 
1. The white species, which Linnaeus calls 
platalea leucorodia, is about the size of a 
heron, but somewhat shorter in the neck and 
legs. The bill is more than half a foot long, 
and, like that of the rest of the genus, is 
shaped like a spoon : the colour of the bill is 
very various, being in some birds black, in 
others brown ; the plumage is entirely white, 
though there have been specimens where the 
quills were tipped with black; the legs are 
generally either black or of a greyish-brown 
colour ; between the toes there is a mem- 
brane connected to the outer one as far as 
the second joint, and to the inner as far as 
the first. 
This bird is found in various parts of the 
Old Continent, and from the Ferro isles near 
Iceland to the Cape of Good Hope. It fre- 
4 
j quents the neighbourhood of the sea, and ha's 
’ been met with on the coasts of France; at 
i Sevenhuvs, near Leyden, once in great plen- 
ty, annually breeding in a wood there. The 
nest is placed on high trees near the sea-side. 
The female lays three or four white eggs, 
powdered with a few pale-red spots, and of 
the size of those of a hen. They are very- 
noisy during breeding-time, -like our rooks; 
are seldom found high up the rivers, chiefly 
frequenting the mouths of them. Their food 
is fish, which they are said not unfrequent ‘y 
to take from other birds, in the manner of the 
bald eagle; also mussels and other shell-fish, 
being found in greatest numbers where these 
are plenty; and they will also devour frogs 
and shakes, and even grass and weeds, which 
grow in the water, as well as the roots of 
reeds. They are migratory, retiring to the 
warmer parts as the winter approaches, and 
are rarely seen in England. Their flesh is 
said to have the flavour of a goose, and is 
eaten by some ; and the young birds have 
been thought good food. 
2. The roseate species, or platalea ajaja, is 
less than the white. The bill is marked all 
round with a furrow parallel to the edge, and 
is of a greyish-white colour, so transparent as 
to show the ramification of the blood-vessels- 
belonging to it: the forehead is of a whitish 
colour between the bill, and eyes, and throat ; 
the plumage is a fine rose-colour, deepest on 
the wings. A variety of this species is entire- 
ly of a beautiful red colour, having a coliar 
of black at the lower part o£ the neck ; the- 
irides are red. It is said to be of a blackish 
ehesnut the first year, becomes rose-coloured 
the second, and -of a deep scarlet the third. 
It lives on small fish. 
3. The dwarf species, or platalea pigmea, 
is about the size of a sparrow. The bill is 
black, longer than the head, flat at the end, 
and nearly of a rhomboidal form ; the body 
is brown above and white beneath. It in bab- 
bits Surinam and Guiana. 
PLATANUS, the plane-tree, a genus of 
the polyandria order, in the moncecia class of 
plants. The male calyx is an ament, globu- 
lar ; corolla scarcely apparent ; anthers grow- 
ing round the filament. Female calyx ament, 
globular; corolla many-petalled ; stigma re- 
moved ; seeds roundish, marcomate with the 
style, pappose at the base. The species are: 
1. The orientalis, oriental or Eastern plane- 
1 tree, rises with a very straight smooth branch- 
ing stem to a great Height. It has palmated 
leave's, six or eight inches long and as much 
broad, divided into five large segments ; hav- 
ing the side ones cut into two smaller, green 
above, and pale underneath ; and long pen- 
dulous pedunculi, each sustaining several 
round heads of close-sitting very small flow- 
ers, succeeded by numerous downy seeds, 
collected into round, rough, hard balls. It 
is a native of Asia and many parts of the East, 
and grows in great plenty in the Levant. 
2. The occidentalis, occidental or Western 
plane-tree, rises with a straight smooth stem 
to a great height, branching widely round ; 
it has lobated leaves, seven or eight inches 
long, and from nine or ten to twelve or four- 
teen broad, divided into three large lobes ; 
and very small flowers, collected into round 
heads, succeeded by round rough balls of 
seed. It is a native of Virginia and other 
parts of North America, where it attains an 
enormous size, and is remarkable lor having 
